Why does my brain do this?

I can't figure out why my brain does this.

The above gif has a framerate of ~50 frames per second. Look at the moving white circle. It runs pretty smoothly doesn't it. (If it doesn't, stop using Internet Explorer)
The individual frames of this gif, are not motion blurred. You can see this, by focusing your vision to the little red dot in the middle. As the white circle moves past it, you can see the individual frames in tiny glimpses, and see that they are really sharp.
Now why does the circle look really smooth when you track its movement with your eyes, then?
Maybe it's the high framerate of 50fps?
I made a couple of tests, and nope.
It's the brain, doing some sort of sorcery.

Check out the image above. This image has a frame rate of 25fps. Almost the same as majority of the movies we watch (which is 24fps).
You can see it yourself by looking at the red dot, and noticing that the gaps between the circles are much bigger, and the motion is more stuttering, compared to the first image.
But track the circle again with your eyes. The motion is still smooth, and motion blurred. The blur is actually much stronger!
As if it was stretching along faster speed.

Now, how far can i take this?
Let's split the frame rate again, to 12,5 fps, which is about the fps used in most traditional animation films.
It's kinda jaggy already.
Tracking the circle with your vision, it still blurs and stretches it as it accelerates.
I've wondered this many times, when moving the mouse cursor. Following it blurs it, and not following it makes me just see individual cursors all over the screen.

I pushed the limits and made a version with only 7fps, and it STILL happens (altough i have to say the blur and stretch is tarting to look really weird at that moment)
The only conclusion I came to, is that the brain somehow interpolates it's own motion blur and a sense of continuous motion, even when the movement is really jagged.
I did know this beforehand, (after all, I work in motion graphics,) but I did never expect it to be this concrete.
And I cant figure out why this is happening. It's mindblowing!

But there are a couple things that make this mysterious.
It doesn't work on vertical motion.
The above image is the same as the 25fps image, just rotated 90 degrees. The blur and the stretching is not nearly the same.

Also, this contradicts the motion blurring, in real life objects.
IRL if you focus your vision on a spot, and something goes by, it blurs out, like in the image above, you can't see if it's my hand or wiener that passes the camera, as it's so blurred.
While if you track the motion of your hand (or wiener) with your eyes, the hand stays in focus, not getting blurred or stretched.

I made these images to try to figure out what my brain does to blur sequential frames, representing a moving object, when tracked by the eye.
I'm still kinda amazed of this.